Add microbenchmarks to flaky repos

I will update the revisions of the rest of the repos to be
"refs/heads/master" in a future CL.

BUG=b/170239624
TEST=repo init and sync

Change-Id: Ic4dc690ac7b782b990f9ecb1909ec3ca17230c1f
diff --git a/flaky_repos.xml b/flaky_repos.xml
index d708b55..e1b6458 100644
--- a/flaky_repos.xml
+++ b/flaky_repos.xml
@@ -49,5 +49,9 @@
            name="chromiumos/platform/fw-testing-configs"
            revision="7ed9632bfe31c5ab7f403f95194c1d8047999374"
            remote="chromium" />
+  <project path="src/platform/microbenchmarks"
+           name="chromiumos/platform/microbenchmarks"
+           revision="refs/heads/master"
+           remote="chromium" />
 
 </manifest>